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Window sill flashing requirements - houston, texas region

Hey guys,

I have a house being built and i believe that the window sill flashing is installed incorrectly. I couldn't find anything online regarding the manufactures installation instructions (Builders FirstSource - 5700 series windows) or any state, local or regional specifications regarding widely accepted practices, rule, laws of how to install window flashing. I couldn't find any definitive answers and came here to find clarity and peace of mind.

My builder is using a non-adhesive poly and didn't run the poly vertical, thereby encompassing the base and the side of the interior portion of the window - the base corners.

My question is 1) is an adhered membrane required (should he use a 'flex wrap of sorts' with adhered backing) and 2) is the poly suppose to run vertical (at least a few inches vertical) leaving the corner of the base of the window, properly protected against outside and inside condensation?

Re: Window sill flashing requirements - houston, texas region

Raymond,

Thanks for your reply. Would it meet *minimum* state, national or international laws, rules or standards and does it have to extend upwards a few inches in the base corners of the window? Also, i just read that an adhesive membrane is voluntary per IRC R703.8/AAMA 711, as i assume because of the wording "voluntary specification for self-adhering flashing...etc". Im I correct?

Also I see that IRC R613.1 requires that windows be 'installed and flashed according to manufactures instructions'. So what I am reading is, though its not mandatory, it becomes mandatory, if and only if, its per manufactures instructions?

Re: Window sill flashing requirements - houston, texas region

IF you google "Builders First Choice Series 5700 Window" you should come up with a URL for a PDF document for the window which, hopefully, would include installation instructions. Although, it could be just a sales brochure. Start downloading it before you go to bed. They must have a really really slow server. Or, call them locally or the corporate office. Maybe they can email it to you or give you a definitive answer on the phone.

The above statements are expressed solely as my opinion and in all probability will conflict with someone else's.
Stu, Fredericksburg VA

Re: Window sill flashing requirements - houston, texas region

When you said Texas I waited for the Texas guys to respond as they are more familiar with the requirements there.

I looked Builders First Source up on their web page and they indicated that they had various product approvals, including Florida, so I looked them up in the Florida Product Approval search and ... they had a picture window approved under the 2007 Florida Building Code but do not have anything approved under the 2010 Florida Building Code, and their product approval was of limited help anyway.

I found this nice video which shows one method of flashing (actually shows two variations of that one method). This method uses a preformed plastic corner flashing, the other common method is to use a flexible flashing tape for the corner flashing, other than that, the rest of the window is flashed basically the same as shown in the video.

The method I prefer is a combination of the A1 and B1 methods shown in the video in that the flashing is placed on the wall, the window with sealant placed against that flashing, then the excess sealant removed and another piece of flashing placed over the window fin - kind of like wearing a belt and suspenders.

There are other, but similar, ways to flash a window, but the intent is always the same - keep water out.

The "correct" way is the way the manufacturer of the window specifies, missing that then the way the building wrap and/or flashing membrane specifies - using the most restrictive of them.

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